No audio on trasferred calls and no hold music

I having trouble with the 3CX server v 8. When calls come in and are put on hold, there is silence - the hold music cannot be heard. I've test this with internal and external calls - both dont work. Also when calls are transferred to another extension, the audio drops. The call stays live, but there is no audio (in or out). Normal internal calls are ok, its only when external calls are transferred to other extensions. The 3CX server has been set as a DMZ on the network, so ports shouldn't be an issue.

I have the line dumping the call to a queue and then ringing the members. The issue is that the call is answered and shows answered in the admin console, yet there is no audio to the end user and the handsets don't ring.